It is often desirable to be able to determine the distance to a surface or object without actually touching the surface or object itself. In the field of process controls, for example, it may be desirable to determine the placement of machine parts, materials, sheets, or irregularly shaped objects without using tape measures, rules, or other normal contact like devices. In the field of photography it is desirable to be able to automatically focus the camera on objects at a remote distance from the camera.
Many optical devices have been devised in the prior art for determining the distance to such remote objects, most of which have been based upon the principle of triangulation wherein light reflected from the object travels over two separate paths so as to be received upon spaced apart detectors and the images they produce compared to determine the distance to the remote object. In other devices a beam of energy is transmitted to the object and the return energy is either measured for the angle in which the reflection occurred or the time elapsed from the sending to receiving of the energy. In my application Ser. No. 675,665, filed Nov. 28, 1984 and assigned to the assignee of the present invention, I disclose a surface position sensor in which a beam of energy is reflected from a surface and passed through an aperture so as to be received along the length of the detector at a position corresponding to the surface position. Other examples of surface position sensors and similar apparatus in the prior art may be seen in the Winslow Palmer U.S. Pat. No. 2,651,771 issued Sept. 8, 1953, the Donald Harvey U.S. Pat. No. 4,065,778 issued Dec. 27, 1977, the Akira Takahashi U.S. Pat. No. 4,479,706 issued Oct. 30, 1984, and the Arthur Winter U.S. Pat. No. 4,473,285 issued Sept. 25, 1984.
One major difficulty with triangulation type systems is that they must have very tight mechanical tolerances which makes them more costly to build and require more care in handling and use than may be desired. The systems which time a beam from transmission to reception are very costly, extremely complex and usually quite large. Ultrasonic types have the additional problem of being subject to interference in factory conditions and being quite bulky.